The invention relates to a method for decorating substrates, more particularly packaging made from unlacquered or lacquered glass, plastic, paper, or cardboard, and also to a decorated substrate produced preferably by such a method.
To decorate, for example, drinking glasses or glass bottles, it is known practice to print them, particularly by a screen printing process, with UV-curable glass printing inks. In this case it is possible to print different-colored printing inks at a number of printing stations arranged in series, in order thus to generate an overall printing image which is composed of different printed patterns. In the printing of glass it is critical to achieve effective adhesion and scratch resistance, chemical resistance, and wet adhesion of the printed pattern. Very good results in this context can be obtained with UV-curable glass printing inks and glass print varnishes from the applicant, in accordance with EP 1 806 327 B1. For the chromatic hues (yellow, orange, red, blue, and green) and also for black and white, very brilliant shades can be achieved. Metallic shades are produced typically from bronzes (silver metallic from aluminum bronzes, gold from CuZn, bronzes and colored metallic bronzes by overcoating with high-transparency chromatic colors such as yellow or red, for example, etc. A disadvantage here for the beverage and cosmetics industries is the inadequate brilliance of the printed metallic shades. Nowadays, therefore, for the decoration of drinking glasses of high-quality appearance, “ceramic printing inks” (known as bright precious metal preparations; see Technical Information No. 1.4/4 from e.g. W. C. Heraeus, Heraeusstrasse 12-14, D-62540 Hanau), which exhibit extremely high brilliance after stoving, continue to be used. Disadvantages of these “ceramic printing inks” are the very high price due to the use of precious metals, the high temperatures (400-700° C.) needed for the stoving operation, and the cost and inconvenience of monitoring the stoving operation. Alternatively it is also possible to use thermoplastic bright precious metal preparations and decorative colors (see Technical Information No. 1.22/4 from W. C. Heraeus). A disadvantage of these systems is that the thermoplastic bright precious metal preparations and decorative colors are solid at room temperature and must be heated before printing to around 65-75° C. so that they become printable. In addition, they also still possess all of the disadvantages mentioned for the “ceramic inks”.
With increasing frequency, therefore, substrates, and especially glass bottles, have been decorated using a hot stamping process, for which purpose a hot stamping foil is pressed under pressure and temperature against the substrate. Hot stamping using hot stamping foils is much more economic than the above processes, and provides highly bright coatings virtually comparable with the bright precious metal preparations. Temperatures utilized for hot stamping in the prior art are between 220° C. and 300° C., in order to ensure optimum transfer of the hot stamping foil to the UV-curing glass printing ink or glass print varnish, respectively.
The hot stamping foil here generally comprises, on a side facing the substrate, a heat-activated bonding layer, on which is located in turn the decorative coating to be applied by stamping. Located between the decorative coating and a backing foil, as for example a polyester foil, of the hot stamping foil there is a release layer to facilitate detachment of the backing foil from the stamped coating after the end of the stamping procedure.
In the case in particular of direct stamping onto glass substrates, the adhesion of the decorative coating or of the heat-activated bonding layer of the hot stamping foil is not sufficient for industrial applications.
Disclosed for this purpose has been the application to the glass substrate, first of all, of what is called an adhesive printing ink in the form of a pattern, onto which the decorative coating is then stamped. Processes of this kind are described for example in EP 06 263 54 B1 (Kamen et al.) and in the Japanese patent publications it cites, No. JP-A 59 184 746 and No. JP-A 57 152 992. A disadvantage of EP 06 263 54 B1 is that, with the processes set out therein, the printing inks do not adhere to the glass substrate to the degree required for commercial purposes (see also DE 695 18 016 T2 from Kamen et al., section 3). With regard to other known, printable adhesive inks as adhesion promoter layer between glass substrate and hot stamping foil, reference is made, for example, to U.S. Pat. No. 5,391,247 A and also to U.S. Pat. No. 5,585,153 A. Latter adhesive inks are radiation-curable. With these known adhesive printing inks there is the problem of low reactivity (examples 1, 2 and 4), a comparatively low scratch resistance, and a comparatively low chemical resistance, for the case, for instance, where hot stamping is to be applied to perfume bottles or cosmetics bottles.
A further problem exists with these processes if complicated decorations are desired which are to have not only a hot-stamped coating but also a printed pattern, as for example a colored printed pattern, adjacently, i.e., in a region adjacent to the coating. In order to avoid the hot stamping foil or decorative coating thereon adhering to all of the printed patterns, it will be necessary, in order to obtain a correspondingly complicated decoration, to use hot stamping dies whose peripheral contour would have to match the contour of the coating to be stamped, in order to prevent the hot stamping foil from being pressed against printed patterns that were not to be stamped. The use of so-called continuous stamping processes, operating with a rotating stamping roll, would not be possible without stamping all of the printed patterns. The use of stamping dies is disadvantageous, however, for a number of reasons. For instance, a dedicated die must be produced and used for each form of coating to be stamped. Furthermore, the operation of hot stamping using a stamping die is slower and more costly.
DE 199 51 404 A1 discloses a method for producing the cover plate of an illuminated advertising unit. For this purpose, first of all, a color pattern is printed onto a substrate, and a high-transparency clear varnish is applied congruently to this pattern. In a subsequent step, a stamping foil is applied by stamping, this foil not adhering to the clear varnish, thus resulting in an overall image which consists of the stamping foil and of the regions left blank over the clear varnish.
DE 10 2004 041 868 B3 describes a transfer foil for in-mold labeling processes, the transfer foil having structural elements for the three-dimensional structuring of injection-molded parts.